This invention relates generally to liquid phase epitaxial processes for III-V semiconductor compounds, and, more particularly, to processes of this kind that produce high-resistance layers of such III-V compounds as indium phosphide, indium gallium arsenide and indium gallium arsenide phosphide.
Liquid phase epitaxy is a popular technique for growing individual high-quality crystalline layers in numerous different multiple-layer semiconductor devices. If is frequently desirable that such layers be semi-insulating, i.e., have resistivities that exceed about 1.times.10.sup.33 or 1.times.10.sup.4 ohm-centimeters. This facilitates monolithic integration of different kinds of devices on a common substrate.
High-resistivity epitaxial layers are particularly useful for III-V compounds such as indium phosphide, indium gallium arsenide and indium gallium arsenide phosphide, which are especially adapted for use as optoelectronic emitters and detectors useful in optical fiber communications. An example of the use of such a high-resistivity layer in a laser/FET device using indium phosphide is disclosed in a copending and commonly-assigned application for U.S. patent, Ser. No. 506,684, filed June 21, 1983 in the names of H. D. Law et al. and entitled "Integrated Laser and Field Effect Transistor."
In one known prior art process for growing a semi-insulating III-V layer using liquid phase epitaxy, chromium is used as a deep level dopant for a gallium arsenide compound. The chromium dopant serves to trap free electrons introduced by background impurities and thereby increase the material's resistivity. Although indium phosphide, indium gallium arsenide and indium gallium arsenide phosphide are likewise III-V compounds, a chromium dopant will have a substantially different effect in them. This is because chromium does not lie in as deep a position in the band gap of these three compounds as it does in gallium arsenide, whereby it does not operate to trap as many free electrons. The limited resistivity that can be achieved for these chromium-doped compounds is believed to be low enough as to make them of limited commercial value.
Bulk-grown crystals of iron-doped and cobalt-doped indium phosphide having high resistivity have been produced in the past. In these crystals, the iron and cobalt serve as deep level traps for free electrons introduced by background impurities. Since the crystals are formed only in a bulk process, however, it has not been possible to utilize them as intermediate layers of a complex multiple-layer device.
It should therefore be appreciated that there is still a need for an epitaxial growth process for particular use in growing high-resistivity layers of III-V semiconductor compounds such as indium phosphide, indium gallium arsenide and indium gallium arsenide phosphide. In particular, there is a need for such a process that can be performed using conventional apparatus. The present invention fulfills this need.